This invention relates to an improved method for bonding objects together.
Metallic objects to be bonded together with a synthetic resin structural adhesive such as an epoxy resin adhesive, for example, objects containing iron or steel, conventionally have their surfaces to be bonded pre-treated in order to improve bonding strength and prevent corrosion of their surfaces at the adhesive bond.
Such methods of pre-treatment can include either a physical method or a chemical method, or both. Physical methods include heating the surfaces to remove fats and oils, and polishing the surfaces by using a sander or grinder. Chemical methods include the removal of fats and oils with a swab or gauze impregnated for example with an organic solvent such as acetone or trichloroethylene.
However, these conventional methods are insufficient to activate the bonding interface of the objects and consequently, it is quite difficult to bond the objects together to obtain a satisfactory bond strength, without a gap between the surfaces and the adhesive. Furthermore, when the objects thus bonded are subjected to severely corrosive conditions, e.g. 50.degree. C. and 100% humidity for one month, hydroxides or oxides are formed on the bonding interface between the objects and the adhesive and the objects are apt to separate at the bonding interface.